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NMR Biomed. 2017 Aug;30(8). doi: 10.1002/nbm.3725. Epub 2017 Apr 3.

Retrospective correction of frequency drift in spectral editing: The GABA editing example.

Author information

1
Magnetic Resonance Spectroscopy Core Facility, NIMH-Intramural Research Program (IRP), National Institute of Mental Health, National Institutes of Health, Bethesda, MD, USA.
2
Clinical and Translational Neuroscience Branch, NIMH-Intramural Research Program (IRP), National Institute of Mental Health, National Institutes of Health, Bethesda, MD, USA.
3
Molecular Imaging Branch, NIMH-Intramural Research Program (IRP), National Institute of Mental Health, National Institutes of Health, Bethesda, MD, USA.

Abstract

GABA levels can be measured using proton MRS with a two-step editing sequence. However due to the low concentration of GABA, long acquisition time is usually needed to achieve sufficient SNR to detect small differences in many psychiatric disorders. During this long scan time the frequency offset of the measured voxel can change because of magnetic field drift and patient movement. This drift will change the frequency of the editing pulse relative to that of metabolites, leading to errors in quantification. In this article we describe a retrospective method to correct for frequency drift in spectral editing. A series of reference signals for each metabolite was generated for a range of frequency offsets and then averaged together based on the history of frequency changes over the scan. These customized basis sets were used to fit the in vivo data. Our results demonstrate the effectiveness of the correction method and the remarkable robustness of a GABA editing technique with a top hat editing profile in the presence of frequency drift.

KEYWORDS:

GABA editing; drift; magnetic resonance spectroscopy; retrospective correction

PMID:
28370463
PMCID:
PMC5511084
DOI:
10.1002/nbm.3725
[Indexed for MEDLINE]
Free PMC Article

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